In recent years, in the fields of production of medicines, gene therapy, regenerative medicine, immunotherapy or the like, it is required to cultivate efficiently a large amount of cells, tissues, microorganisms or the like in an artificial environment.
In such cultivation of a large amount of cells, when floating cells are cultured, there has been a demand for counting the number of cultured cells in order to grasp a change in the number of cells with the passage of time and a change in proliferation efficiency. However, conventionally, counting the number of cultured cells accurately encountered various problems.
Specifically, in proliferation of floating cells, there are cell clusters formed by three-dimensional aggregation of cells and individual cells that are present individually.
Conventionally, counting was conducted by a method wherein these cultured cells are photographed from above or from below, and then, based on the projected area of the cultured cells in an acquired image, the projected area of a cell cluster is divided by the average area of individual cells, whereby the number of cells is counted.
However, since a cell cluster is three-dimensional, the number of cells thus counted is smaller than the actual number of cells in a cell cluster. Further, if individual cells are assembled densely in a planar manner, the number of cells obtained by dividing the projected area of an individual cell by the average cell area of individual cells is counted in a number larger than the actual number of individual cells. Accordingly, there was a problem that the number of cells counted based on the projected area of the cultured cells is not accurate.
On the other hand, in order to obtain an accurate number of cells, it can be considered to count the number of cells by completely pulling apart a cell cluster.
However, in general, there is a further problem that excessive pulling apart of a cell cluster causes lowering of the proliferation efficiency. For this reason, conventionally, it was impossible to conduct accurate counting during cultivation, and an accurate counting was possible only at the time of collecting cells.
Here, as one of conventional methods of counting the number of cultured cells, the cell counting method disclosed in Patent Document 1 can be given. In this method, an observation image of cultured cells that are present in a culture container is acquired, and the ratio of an area occupied by cultured cells in the thus obtained observation image is calculated as an occupied area ratio. Then, based on the thus calculated occupied area ratio and a predetermined relational formula, the number of cultured cells present in the culture container is calculated.